System and method for producing synthetic diamond

ABSTRACT

Synthetic monocrystalline diamond compositions having one or more monocrystalline diamond layers formed by chemical vapor deposition, the layers including one or more layers having an increased concentration of one or more impurities (such as boron and/or isotopes of carbon), as compared to other layers or comparable layers without such impurities. Such compositions provide an improved combination of properties, including color, strength, velocity of sound, electrical conductivity, and control of defects. A related method for preparing such a composition is also described., as well as a system for use in performing such a method, and articles incorporating such a composition.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/009,481, filed Oct. 29, 2004, which is a continuation U.S.patent application Ser. No. 10/328,987, filed Dec. 24, 2002, which is acontinuation of U.S. patent application Ser. No. 09/312,326, filed May14, 1999, which is a continuation of U.S. Provisional Patent ApplicationSer. No. 60/085,542, filed May 15, 1998, the entire disclosure of whichis incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to synthetic diamonds and to methods forpreparing and using synthetic monocrystalline diamonds. In particular,the invention relates to monocrystalline diamonds produced by the methodof chemical vapor deposition, including the role of impurities such asnitrogen, phosphorous, boron, and the isotope ¹³C in such compositions.

BACKGROUND OF THE INVENTION

Monocrystalline diamonds, as found in nature, can be classifiedaccording to color, chemical purity and end use. The majority ofmonocrystalline diamonds are colored, and contain nitrogen as animpurity, and are thereby used primarily for industrial purposes; thesewould be classified as type Ia and Ib. The majority of gem diamonds(which are all considered “monocrystalline” diamonds) are colorless orvarious light colors and contain little or no nitrogen impurities; andwould be classified as type IIa. Types Ia, Ib and IIa are electricalinsulators. A rare form of monocrystalline diamond (classified as typeIIb) contains boron as an impurity, is blue in color and is asemiconductor. In nature these characteristics are uncontrolled andtherefore the color, impurity level and electrical characteristics areunpredictable and cannot be utilized to produce large volumes ofspecialized articles in a predictable manner.

Monocrystalline diamond provides a wide and useful range of extremeproperties, including hardness, coefficient of thermal expansion,chemical inertness and wear resistance, low friction, and high thermalconductivity. Generally monocrystalline diamond is also electricallyinsulating and optically transparent from the ultra-violet (UV) to thefar infrared (IR), with the only absorption being carbon-carbon bandsfrom about 2.5 μm to 6 μm. Given these properties, monocrystallinediamonds find use in many diverse applications including, as heatspreaders, abrasives, cutting tools, wire dies, optical windows, and asinserts and/or wear-resistant coatings for cutting tools. Theengineering and industrial uses of diamonds have been hampered only bythe comparative scarcity of natural monocrystalline diamond. Hence therehas been a long running quest for routes to synthesize monocrystallinediamond in the laboratory.

Synthetic monocrystalline diamonds, for industrial use, can be producedby a variety of methods, including those relying on a “high pressuremethod” and those involving controlled vapor deposition (CVD). Diamondproduced by either the “high pressure method” or the CVD method can beproduced as monocrystalline diamond or polycrystalline diamond. Highpressure diamond is usually formed as micron sized crystals, which canbe used as grit or loose abrasive, or set into metal or resin forcutting, grinding or other applications.

Both methods, i.e., “high pressure method” and “CVD method” make itpossible to control the properties to a high degree and thereby controlthe properties of color, impurity level and electrical characteristicson a theoretical level. However, on a practical level, in order tomanufacture useful objects by the “high pressure method”, there arelimitations imposed by the presence or absence of impurities. As anexample, it has been suggested that the addition of nitrogen mightassist in the growth of large crystals, although the elimination ofnitrogen, or the addition of boron, can make it more difficult to growlarge crystals. In addition, it appears that it is not possible to makemonocrystalline structures having layers of varied composition withouthaving to remove the seed crystal from the reactor after each layer isgrown, and then replacing the seed crystal in the reactor in order togrow a subsequent layer having a different composition. Moreover, largeseeds cannot be accommodated in the “high pressure method”. In the CVDmethod, most work has been confined to production of polycrystallinediamond, as opposed to the growth and control of single crystals.

It is actually difficult and expensive to produce high quality puremonocrystalline diamond by the high pressure method. It has been shownthat the addition of boron to a synthetic monocrystalline orpolycrystalline diamond makes it useful for constructing a semiconductordevice, a strain gauge or other electrical device althoughmonocrystalline diamond is to be preferred. See U.S. Pat. No. 5,635,258.See also, W. Ebert, et al. “Epitaxial Diamond Schottky Barrier DiodeWith On/Off Current Ratios in excess of 107 at High Temperatures”,Proceedings of IEDM, pp. 419-422 (1994), Published by IEEE, and S.Sahli, et al., “Piezoelectric Gauge Factor Measured at Different Fieldsand Temperatures”, pp. 95-98, Applications of Diamond Films and RelatedMaterials, A. Feldman, et al. editors, NIST Special Publications 885. Socalled ‘industrial diamond’ has been synthesized commercially for over30 years using high-pressure high-temperature (HPHT) techniques, inwhich monocrystalline diamond is crystallized from metal solvated carbonat pressures of about 50 to 100 kbar and temperatures of about 1800 to2300K. In the high pressure method the crystals grow in a threedimensional manner and the crystal is all of one impurity level, exceptfor possible discontinuities arising from fluctuations in the growthcycle. See, for example, R. C. Bums and G. Davis, “Growth of SyntheticDiamond”, pp. 396-422, The Properties of Natural and Synthetic Diamond,J. E. Field, editor, Academic Press (1992), U.S. Pat. Nos. 3,850,591 and4,034,066.

Interest in diamond has been further increased by the much more recentdiscovery that it is possible to produce polycrystalline diamond films,or coatings, by a wide variety of chemical vapor deposition (CVD)techniques using, as process gases, nothing more exotic than ahydrocarbon gas (typically methane) in an excess of atomic hydrogen. CVDdiamond grows two dimensionally, layer by layer and it is thereforepossible to build up a bulk crystal (or plate or film) which can be of asingle composition or composed of layers of many compositions (called a“structure”). CVD diamond grown in this manner can show mechanical,tribological, and even electronic properties comparable to those ofnatural diamond. See, for example, Y. Sato and M. Kamo, “Synthesis ofDiamond From the Vapor Phase”, pp. 423-469, The Properties of Naturaland Synthetic Diamond, J. E. Field, editor, Academic Press (1992). Seealso US patents for background; U.S. Pat. Nos. 4,940,015; 5,135,730;5,387,310; 5,314,652; 4,905,227; and 4,767,608.

There is currently much optimism that it will prove possible to scale-upCVD methods to such an extent that they will provide an economicallyviable alternative to the traditional high pressure methods, e.g., forproducing diamond abrasives and heat spreaders. The ability to coatlarge surface areas with a continuous film of diamond, in turn, willopen up new potential applications for the CVD-prepared materials.Today, however, the production of monocrystalline diamond by the CVDprocess is considerably less mature than high pressure, and theresultant materials tend to have higher defect levels and smaller sizes.

Chemical vapor deposition, as its name implies, involves a gas-phasechemical reaction occurring above a solid surface, which causesdeposition onto that surface. All CVD techniques for producing diamondfilms require a means of activating gas-phase carbon-containingprecursor molecules. This generally involves thermal (e.g., hotfilament) or plasma (e.g., D.C., R.F., or microwave) activation, or theuse of a combustion flame (oxyacetylene or plasma torches). Two of themore popular experimental methods include the use of a hot filamentreactor, and the use of a microwave plasma enhanced reactor. While eachmethod differs in detail, they all share features in common. Forexample, growth of diamond (rather than deposition of other, lesswell-defined, forms of carbon) normally requires that the substrate bemaintained at a temperature in the range of 1000-1400 K, and that theprecursor gas be diluted in an excess of hydrogen (typical CH₄ mixingratio ˜1-2 vol %).

The resulting films are usually polycrystalline (unless amonocrystalline diamond seed is provided) with a morphology that issensitive to the precise growth conditions. Growth rates for the variousdeposition processes vary considerably, and it is usually found thathigher growth rates can be achieved only at the expense of acorresponding loss of film quality. Quality is generally taken to implysome measure of factors such as the ratio of sp3 (diamond) to sp2-bonded(graphite) carbon in the sample, the composition (e.g. C—C versus C—Hbond content) and the crystallinity. In general, combustion methodsdeposit diamond at high rates (typically 100 μm/hr to 250 μm/hr), butoften only over very small, localized areas and with poor processcontrol, thereby leading to poor quality films. In contrast, the hotfilament and plasma methods tend to provide have much slower growthrates (0.1-10 μm/hr), but produce high quality films.

One of the great challenges facing researchers in CVD diamond technologyis to increase the growth rates to economically viable rates, (to thelevel of 100+μm/h, or even one or more mm/hr) without compromising filmquality. Progress continues to be made in the use of microwavedeposition reactors, since the deposition rate has been found to scaleapproximately linearly with applied microwave power. Currently, thetypical power rating for a microwave reactor is ˜5 kW, but the nextgeneration of such reactors have power ratings up to 50-80 kW. Thisgives a much more realistic deposition rate for the diamond, but for amuch greater cost, of course.

Thermodynamically, graphite, not diamond, is the stable form of solidcarbon at ambient pressures and temperatures. The fact that diamondfilms can be formed by CVD techniques is inextricably linked to thepresence of hydrogen atoms, which are generated as a result of the gasbeing ‘activated’, either thermally or via electron bombardment. These Hatoms are believed to play a number of crucial roles in the CVD process:They undergo H abstraction reactions with stable gas-phase hydrocarbonmolecules, producing highly reactive carbon-containing radical species.This is important, since stable hydrocarbon molecules do not react tocause diamond growth. The reactive radicals, especially methyl, CH₃, candiffuse to the substrate surface and react, forming the C—C bondnecessary to propagate the diamond lattice. H-atoms terminate the‘dangling’ carbon bonds on the growing diamond surface and prevent themfrom cross-linking, thereby reconstructing to a graphite-like surface.Atomic hydrogen etches both diamond and graphite but, under typical CVDconditions, the rate of diamond growth exceeds its etch rate, while forother forms of carbon (graphite, for example) the converse is true. Thisis believed to be the basis for the preferential deposition of diamondrather than graphite.

One major problem receiving a lot of attention is the mechanism ofheteroepitaxial growth, that is, the initial stages by which diamondnucleates upon a non-diamond substrate. Several studies have shown thatpre-abrasion of non-diamond substrates reduces the induction time fornucleation and increases the density of nucleation sites. Enhancedgrowth rates inevitably follow since formation of a continuous diamondfilm is essentially a process of crystallization, proceeding vianucleation, followed by three-dimensional growth of the variousmicrocrystallites to the point where they eventually coalesce.

The abrasion process is usually carried out by polishing the substratewith an abrasive grit, usually diamond powder of 0.1 μm to 10 μmparticle size, either mechanically or by ultrasonic agitation.Regardless of the abrasion method, however, the need to damage thesurface in such a poorly defined manner, prior to deposition, mayseverely inhibit the use of CVD diamond for applications in areas suchas the electronics industry, where circuit geometries are frequently ona submicron scale. This concern has led to a search for morecontrollable methods of enhancing nucleation, such as ion bombardment.Ion bombardment can be performed in a microwave deposition reactor, bysimply adding a negative bias of a few hundred volts to the substrateand allowing the ions to (i) damage the surface, (ii) implant into thelattice, and (iii) form a carbide interlayer.

These methods are in direct contrast to the production ofmonocrystalline diamond by CVD, e.g., where a polished monocrystallinediamond is used as a seed crystal and the structure of that seed crystalis reproduced in the new monocrystalline diamond grown on the seed. Theresulting monocrystalline diamond has superior properties topolycrystalline diamond for most industrial, optical, electronic andconsumer applications.

A variety of methods have been described for use in preparing syntheticdiamonds. See, for example, U.S. Pat. Nos. 5,587,210, 5,273,731 and5,110,579. Most of the scientific research effort into CVD diamondtechnology has been concentrated within the past five years yet,already, some of the more immediate applications, such as cutting toolsand heat spreaders, have reached the market-place. Several problems needto be addressed and over come before this technology begins to make asignificant impact however. Growth rates need to be increased (by one ormore orders of magnitude) without loss of film quality. Depositiontemperatures need to be reduced by several hundred degrees, allowing lowmelting point materials to be coated and to increase the number ofsubstrates onto which adherent diamond films can be deposited. A betterunderstanding of the nucleation process is required, hopefully leadingto an elimination of the poorly controlled pre-abrasion step. Substrateareas need to be scaled up, again without loss of uniformity or filmquality. For electronic applications, single crystal diamond films aredesperately needed, along with reliable techniques for patterning andcontrolled n- and p-type doping.

On a related subject, diamond has the highest thermal conductivity ofany known material, with a value on the order of five times that ofcopper metal. High thermal conductivity is a very important property formany applications because it permits heat to be removed rapidly from anarrow source and spread to a larger area where it can be completelyremoved from an operating system.

In the area of materials fabrication (cutting), heat is generated at thecutting tip or edge of a tool as a result of the cutting process. Ifthat heat is not removed the temperature of the cutting tool increasesto the point that it degrades by oxidation, corrosion or fracturing andthe tool becomes unusable. Furthermore, as the tool is degrading, thequality and precision of the part being fabricated degradessignificantly. When a cutting tool is made of diamond, the high thermalconductivity of diamond, heat from the cutting tip or edge is rapidlyremoved from that tip or edge to the tool holder and the temperature ofthe cutting tip or edge runs significantly cooler than comparable toolsmade from other materials such as carbides, oxides, nitrides or borides.Therefore, diamond tools can generally run longer and provide higherquality manufactured parts over a longer period of time than alternativecutting materials (cutting tool patents). In a similar manner, wire diesare made of diamond because they have great resistance to wear andbecause the heat of drawing the wire can rapidly be dissipated from thewire. This results in a longer life for the wire die and higher qualityof wire for a longer length of wire than can be obtained withalternative wire die materials. (wire die patents) point or surfacewhich is generating heat, thereby diamond cutting tools and wire dies toconduct heat away from the cutting surface in tools and the wear surfacein wire dies and promotes longer life by reduced wear and enables ahigher quality part or wire to be fabricated throughout the life of thetool or wire die.

In windows for high power lasers, thermal lensing occurs when light ispartially absorbed by the lens material and the lens material heatscausing a change in index of refraction of the lens material. Since theheat generated by the laser beam must be dissipated to the outersurfaces of the sense there will be a gradient in the index ofrefraction of the material and that will cause the laser beam to bedistorted or to focus or defocus in an uncontrolled manner. Suchuncontrolled distortion will result in uncontrolled cutting or weldingin high power laser fabrication equipment and limit the useful power andthereby the number of applications to which such lasers can be used. Thesame problems arise in the use of high power lasers for communications,fusion power or other applications well known to those who are engagedin the art.

It is apparent that the use of diamond windows in high power lasersystems is highly desirable and would lead to higher power laser cuttersand welders and other applications such as communications. It is alsoapparent that even higher thermal conductivity diamond would result inhigher power lasers becoming feasible. It is further apparent thatbreakdown and damage of the diamond window will be governed by howrapidly heat can be removed from the window, thereby higher thermalconductivity diamond windows would be expected to experience a reducedfailure rate from breakdown and damage.

In semiconductor devices such as solid state laser and high powermicrowave devices a high level of heat is generated in a very smallarea. This heat must be removed or the device temperature will rapidlyrise to the level that the device will cease to operate properly or failcatastrophically. This problem can be alleviated by attaching thesemiconductor device a diamond plate which rapidly removes heat form thesmall area of the device and spreads it to a larger area of a coolingfin or cooling device (P. Hui, et al, Temperature Distribution in a HeatDissipation System Using a Cylindrical Diamond Heat Spreader on a CopperBlock, J. Appl. Phys. 75 (2), 15 Jan. 1994). Diamond has also beensuggested for use to cool three dimensional arrays of semiconductordevices or IC's to produce very high speed three dimensional computerswhere the stacks of chips are to be cooled by contact with diamondplates. (R. Eden, Applications in Computers, Handbook of IndustrialDiamonds and Diamond Films, pp 1073-1102, Editors, Mark Prelas, GalinaPopovici and Louis Bigelow, Marcel Decker, NY, 1998).

In all of these devices and cutting tools, the performance and lifetimeis directly related to the temperature of the active part of the deviceand tool. The operating temperature of the active part of thedevice/tool is directly related to the thermal conductivity of thediamond heat being used. However, the thermal conductivity (TC) ofdiamond is dramatically effected by impurities, crystal defects and bypolycrystallinity. Therefore the performance of a diamond tool or adiamond cooled semiconductor will be directly related to the thermalconductivity of the diamond used. (see M. Seal, “High TechnologyApplications of Diamond”, pp. 608-616, The Properties of Natural andSynthetic Diamond Edited by J. E. Field, Academic Press (1992)).

Polycrystalline diamond typically has the lowest thermal conductivity,nitrogen doped single crystal is higher, followed by pure diamond whichhas the highest. The highest thermal conductivity natural diamond istype IIa which contains little to no nitrogen and has values of thermalconductivity of 2000 to 2500 watt/meter degree Kelvin (W/mK). (see V. INepsha, “Heat Capacity, Conductivity, and Thermal Coefficient ofExpansion”, pgs. 147-192, Handbook of Industrial Diamond and DiamondFilms, M. A. Prelas, G. Popovici, and L. K. Bigelow, Editors, MarcelDekker, Inc. (1998)). Numerous measurements of natural diamond andsynthetic diamond produced by the high temperature high pressure methodshowed that this value of 2000 to 2500 was usually the highestattainable thermal conductivity, and is the accepted value to this day.A TC value of about 2200 was also attained in high qualitypolycrystalline diamond. See, e.g., CVD Diamond: a New EngineeringMaterial for Thermal, Dielectric and Optical Applications, R. S.Sussman, et al., Industrial Diamond Review, 58(578):69-77 (1998).

Thermal conductivity in diamond occurs by phonon-phonon transfer andthermal conductivity is controlled by the mean free path (1) thosephonons in the diamond crystal. Therefore any property of diamond whichcauses a variation in the mean free path of a phonon will cause avariation in thermal conductivity of the diamond. Scattering of phononsreduces the mean free path and phonon scattering can be causedphonon-phonon interactions (ppi), grain boundaries (gb), dislocations(dis), vacancies (vac), impurities (imp), isotopes (iso) and othermechanisms including voids (othr). The mean free path of a phonon isgiven by the equation:

1/|=1/|(ppi)+1/|(gb)+1/|(dis)+1/|(vac)+1/|(imp)+1/|(iso)+1/|(othr)

For an in-depth summary of the theory see U.S. Pat. No. 5,540,904.Carbon exists in three isotopes ¹²C, ¹³C and ¹⁴C. ¹²C is present atlevels of 99 percent in natural diamond, ¹³C and ¹⁴C is so low andradioactive so that it is used for dating in geological or archeologicalsites. Application of the aforementioned theory has led to significantimprovements of the thermal conductivity of diamond crystals andpolycrystalline diamond by reducing the amount of carbon 13 (¹³C) inthese materials and by increasing the grain size in polycrystallinediamond thereby reducing the volume of grain boundaries. By reduction ofthe ¹³C content of single crystal and polycrystalline diamond from 1.1%(as found in natural diamond and naturally occurring diamond precursors)to 0.001% ¹³C the thermal conductivity at room temperature was found toincrease from 2000 W/mK (in natural isotope diamond) to 3300 W/mK inisotopically enriched diamond (U.S. Pat. Nos. 5,540,904, 5,360,479 and5,419,276).

It was also found that the thermal conductivity of diamond could bealtered by changing the purity the diamond starting materials withrespect to the carbon isotopes. For instance, when diamond crystals orpolycrystalline diamond was produced which was 99.999% pure with respectto the ¹²C isotope, the thermal conductivity at room temperatureincreased to 3300 W/mK. It was also concluded that this was indeed thehighest thermal conductivity possible and that since this high thermalconductivity was also observed in polycrystalline diamond, crystallineproperties such as grain boundaries were not a major loss of thermalconductivity. Theoretical analysis of the thermal conductivity ofdiamond was conducted by (P. G. Klemens, Solid State Physics: Advancesin Research and Applications, edited by R. Seitz and D. Tumbill(Academic, New York, 1958) Vol. 7) which showed agreement with the abovecited work in that it predicted that high thermal conductivity wouldoccur in isotopically enriched diamonds. However, this work alsopredicted that the thermal conductivity of pure natural isotopeconcentration diamond should also be 3300 W/mK at room temperature.Since no natural diamond or synthetic diamond has been found which has athermal conductivity higher than 2200 W/mK it was concluded by thoseskilled in the art that either, the theory was wrong or there is someyet unaccounted factor which degrades the thermal conductivity ofnatural isotope concentration diamond.

The ability to increase the thermal conductivity of single crystaldiamond by over 50% from 2300 W/mK to 3300 W/mK or more would offersignificant performance enhancements for diamond cutting tools, diamondwire dies, high power laser windows, high power semiconductor devicessuch as lasers, microwave devices and three dimensional computers orcircuits. The advantages of enhanced thermal conductivity diamond have,to date however, not been applicable to any commercial applicationbecause the cost of producing ¹²C enhanced precursor gasses (typicallymethane gas) is prohibitively high compared to the cost of naturalisotope gasses. Typically, the cost of ¹²C enriched precursors, such asmethane gas, is $75 to $200 per gram, compared with the cost ofunenriched methane at less than $0.01 per gram. Since only 1 to 2% ofthe methane is converted to diamond this would result in a cost ofmaterials for enhance thermal conductivity of $7,500 to $20,000 per gramof diamond crystal produced and the cost for natural isotope rawmaterials at less than $1 per gram of diamond produced. This high costfar overshadows the advantages in tool, wire die, window or deviceperformance obtained and would permit such enhanced thermal conductivitydiamond to be used in only the most demanding and cost tolerant and lowvolume specialty applications.

SUMMARY OF THE INVENTION

The present invention provides synthetic monocrystalline diamondsproviding an improved combination of such properties as thermalconductivity, crystal perfection, coloration, strength, velocity ofsound, fracture toughness, hardness, shape and the like. The improveddiamonds are prepared by a method of controlled vapor deposition (CVD)in which the amounts and/or types of impurities are modified andcarefully controlled, within one or more layers of the diamond, in orderto provide an overall improved product and/or improved process ofpreparing such a product. In one embodiment such impurities include, forinstance, the affirmative addition of impurities such as boron withinone or more layers of a multi-layered diamond, in order to achieve animproved combination of such properties as hardness, fracture toughness,electrical conductivity, optical properties, and crystal perfection. Inan alternative embodiment, the control of such impurities involveslowering nitrogen content in a thick, single-layered diamond, whilemaintaining C isotope levels at natural or near-natural levels, in orderto achieve, among other things, improved thermal conductivity.

In the first embodiment identified above, the present invention providesa synthetic monocrystalline diamond composition comprising one or moremonocrystalline diamond layers formed by chemical vapor deposition, thelayers including one or more layers having an increased concentration ofone or more impurities (such as boron and/or isotopes of carbon), ascompared to other layers or comparable layers without such impurities.Such a composition, provides an improved unique combination ofproperties, including color, strength, velocity of sound, electricalconductivity, and control of defects. In another aspect, the inventionprovides a method of preparing such a diamond, the method involving thesteps of growing a layer of diamond with a designated impurity, growingan additional layer of monocrystalline diamond with different impuritiesand/or impurity levels, and repeating this process with various layersof varied composition and thickness to achieve the desired structure.

In yet another aspect, the invention provides a system for use inperforming such a method, and articles incorporating such a composition.By “doped”, as used herein, it is meant that at least one layer within acomposition of this invention has been grown with an amount of one ormore impurities, e.g., incorporated into the gas stream, in order tobring about an amount of an impurity, such as boron, phosphorous, carbonisotopes, or lithium in the synthetic monocrystal layer, sufficient toproduce a measurable change in the electrical, physical, optical,electronic or crystallographic properties. By “undoped” it is meant thatthe layer has substantially no boron (or other impurities), such thatthe layer has all the attributes described above of pure monocrystallinediamond.

In another aspect, the invention involves a variety of structures thatcan be built from monocrystalline diamond of this invention, e.g., onecomposed of layers containing different concentrations of impurities, aswell as methods that employ such structures. The invention alsodescribes new uses for semiconducting monocrystalline diamond made bythe addition of impurity-doped layers, as well as methods for using andmethods for producing monocrystalline diamond crystals with improvedoptical and electrical properties, and methods for using both undopedand doped monocrystalline diamond plates. All of these methods andcompositions refer to monocrystalline diamond grown by the CVD method.

With regard to the alternative embodiment set forth above, Applicantshave discovered the manner in which monocrystalline diamond can beprepared having a thermal conductivity significantly greater than haspreviously been known for comparable (i.e., non-isotopically enriched,CVD-grown) diamond. Such diamond exhibits, for instance, thermalconductivity of at least about 2300 W/mK, preferably at least about 2500W/mK, and more preferably at least about 2800 W/mK while retaining a ¹³Cisotope content within the normal range (e.g., greater than about 0.1%and more preferably greater than about 0.8%). Such thermoconductivitylevels have only been known or postulated to date for diamonds grown bythe comparatively expensive and technically difficult process known as“isotope enrichment”, where by comparison, the corresponding ¹³C contentis required to be significantly reduced to the range of 0.01% to about0.0001%.

Given the present teaching, however, those skilled in the art will beable to prepare diamond of this embodiment using conventional CVDtechniques and without isotope enrichment, e.g., by growing a thickerdiamond while maintaining the impurity nitrogen at a suitably low level(e.g., less than about 50 ppm, more preferably less than about 20 ppm,even preferably less than about 10 ppm and most preferably less thanabout 5 ppm). The resulting diamond provides significantly improvedproperties in a manner that is significantly less expensive than theclosest known methods in the art.

DETAILED DESCRIPTION

The method and composition of the present invention can take a varietyof embodiments, including the following: The use of diamond in thissection refers to monocrystalline diamond. While not intending to bebound by theory, the method and composition of the present invention, inat least one embodiment, are based on the fact that nitrogen or boronatoms are larger than carbon atoms. Therefore when these elements areadded to the diamond structure, the crystal lattice expands. When highlevels of nitrogen or boron are incorporated in the diamond, the averagedistance between carbon atoms in the diamond becomes measurably largerthan pure diamond. See, for example, A. R. Lang, “Diffraction andImaging Studies of Diamond”, pp. 215-258, The Properties of Natural andSynthetic Diamond, J. E. Field, editor, Academic Press (1992), A. R.Lang, “Dilation, density and nitrogen containing type 1a diamonds:previous work and proposed experiments”, pp. 2239-2244, IPO PublishingLtd., 1993, and O. A. Voronov, A. V. Rahmania, “Cubic Lattice Parameterof Boron Doped Diamond”. Applicant has discovered that this principlecan be advantageously used to provide an improved diamond composition inthe manner described herein. The relationship between nitrogen contentand the resultant increase in the lattice constant is provided by thefollowing equation (see also, A. R. Lang, “Diffraction and ImagingStudies of Diamond”, p. 246, The Properties of Natural and SyntheticDiamond, Edited by J. E. Field, Academic Press (1992)):a=a_(o)×(1+1.4×10−7×[N], with a=lattice constant for doped diamond,a_(o)=lattice constant for pure diamond, and [N]=the nitrogenconcentration in parts per million atomic (ppma).

The relationship between boron content and the resultant increase in thelattice constant is given by the following equation (see F. Brunet, et.al., “Effect of boron doping on the lattice parameter of homoepitaxialdiamond films”, Presented at the 1997 European Diamond Conference,Edinburgh, Scotland, August 3-8, (1997)):

a=a _(o)×(1+1.38×10−7×[B]), for [B]<1525, and a=a_(o)×(1−5.6×10⁻⁴+4.85×10−7×[B],

for [B]>1525, with a=lattice constant for doped diamond, a_(o)=latticeconstant for pure diamond, and [B]=the boron concentration in ppma.

These equations can be used to assist in the design of multi-layerstructures which are lattice matched or which have a layer or layerswith a tailored lattice mismatch. If, for instance, a thin boron dopedor nitrogen doped layer is grown on normal diamond substrate, thesurface spacing of the carbon atoms will be larger than the substrate,therefore, the underlying diamond substrate will be placed incompression but the new surface layer of boron (or nitrogen) dopeddiamond will be in tension. Applicant has found that this results instrengthening the bulk diamond and making it more resistant to crackingor other mechanical failure, while also weakening the diamond surfaceand making it more susceptible to cracking. If, however, an additionallayer of undoped diamond is grown on the doped layer, that undoped layerwill be in compression and the surface will be strengthened.Surprisingly, the resulting composition is thereby strengthened by thesequence of layers. This feature can be used to advantage to strengthena large number of single crystal diamond articles such as cutting tools,surgical knives, microtomes, wire dies and so forth. The strain energydue to lattice mismatch (C-=(a_(o)−a_(f))/a_(o1) with a_(o)=substratelattice constant, a_(f)=layer lattice constant) can be estimated usingthe equation: Energy=t×E×C-²/(1−v), with t=film thickness, E=Young'smodulus, and v=Poisson's ratio (for example, see C. R. M. Grovenor,Microelectronic Materials, p. 139, Adam Hilger (1989)). This equation,along with the equations which give the lattice constant change due toimpurity addition, can be used to produce a layer or layers with atailored strain energy.

Crystals of diamond usually contain dislocations that arediscontinuities in the arrangement of the atoms from perfect order.These dislocations usually travel in straight lines and therefore extendfrom the substrate into the film or crystal grown on the substrate. Ithas been demonstrated on conventional semiconductors that when adislocation intersects with a layer that is in compression or tension,that the dislocation will change direction and run at an angle differentfrom its original direction. (See J. Y. Tsao, B. W. Dodson, S. T.Picraux and D. M. Cornelison, “Critical Stress for Six-Ge(1-x)Strained-Layer Plasticity”, 59 (21) Physical Review Letters, pp.2455-2458, 23 Nov. 1987). By making a series of thin layers that arealternately in compression and tension, the propagation of dislocationscan be reduced or completely halted. (See Y. C. Chen, J. Singh and P. K.Bhattacarya. “Suppression of defect propagation in semiconductors bypseudomorphic layers”, J. Applied Physics, 74 (6), 14 Sep. 1993).Applicants have found that this process can be extended to diamond bygrowing layers that are alternately boron doped (or nitrogen doped) andundoped.

The method of the present invention can be use to preparelow-dislocation or dislocation-free diamond crystals, substrates andstructures. The method can also be used to prepare strain free opticalelements made from low or dislocation free diamond. Strain results inbirefringence that degrades the performance of optical elements such aslenses and windows and gemstones.

The method further permits the production of low-dislocation ordislocation-free substrates for semiconductor devices. It is known insilicon, and has been reported in diamond, that impurities canaccumulate on dislocations that leads to localized degradation of deviceperformance. The present invention therefore also includes higherperformance devices using substrates with low dislocations and made by amethod as described herein.

Diamond plates made entirely of alternating layers of doped and undopeddiamond are also expected to provide increased strength and resistanceto cracking. These would be useful in surgical blades, cutting tools,slicing tools, wire dies and other applications where stress will beapplied.

Another family of products that can be prepared using synthetic diamondcompositions as described herein is based on the fact that high boronconcentration in diamond leads to a blue colored diamond. Diamond platescan be fashioned into small sharp blades which are highly advantageousfor certain types of surgery, including for instance, a surgical bladewhich is heavily doped with boron and blue in color. See U.S. Pat. No.5,713,915 with regard to surgical blades generally. Such a bladeprovides a particular advantage since it is provides better visibilityof the blade; as compared to conventional diamond blades, which aretypically colorless or pale yellow and difficult to see. In addition,the diamond blade surface can be placed in compression, thereby givingit added strength. The boron doped diamond can be provided as the wholevolume of the blade or as a coating on the outer layer or inner layer.

Diamond coloration can also be used to make diamonds which are moreeasily fabricated using laser cutting techniques. The addition of boronresults in an optical absorption in the near infrared which leads tohigher absorption of YAG laser light and this reduces the power levelrequired in fabricating articles by laser cutting. For example, diamondis often shaped by cutting with a YAG laser operating at 1.06 microns.Addition of boron increases the optical absorption at this wavelength,and this can significantly simplify the laser cutting process byallowing use of lower power, which in turn will reduce damage andcracking of the manufactured diamond part. The change in absorption at1.06 microns can be tailored by controlling the amount of boron which isintroduced, and the position of the absorption in the diamond can betailored by the position of the boron layer in a multilayer structure.

Since the boron doped layer can be added at any time in the process, itwill be possible to place the blue coloring inside a transparent sheath,providing the blue coloring while permitting polishing of the outersurface. The blue internal or external diamond layer can be provided forany use where easy visual or optical detection of the diamond isrequired. Alternately, a surgical blade can be made of solid boron dopeddiamond. The color can be varied from light blue to black depending onthe boron concentration.

A third family of applications is based on the fact that boron dopingleads to electrical conductivity. Applications include the following:

1. Boron doped diamond undergoes a change in electrical resistivity whenit is placed under compression or tension and when it changestemperature. Therefore, the method of the present invention can be usedto coat a single crystal diamond tool with boron doped single crystaldiamond, and measure the stress on the tool under operation and itstemperature. This, in turn, can be used to provide an in situ sensor formonitoring and controlling a machining operation, permitting it tooperate in an optimal manner. This feature can also be adapted for usein providing mechanically guided surgical blades for minimally evasivetypes of surgery.

2. The use of conducting, boron doped diamond in surgery will reduce thepossibility of electrical discharge from the surgical blade caused bystatic electricity and thereby prevent damage to the patient orsurrounding electrical monitoring equipment or implanted devices such aspacemakers.

3. Diamond can be used to slit materials such as plastic film, paper andthe like or cut tissue thin sections in a microtome. A common problemwith such process is the accumulation of static electricity that leadsto catastrophic electrical discharge or accumulation of dust, dirt andcutting residue on the cut surface. Boron doped diamond surfaces on thetool can be used to prevent such static buildup. In some cases it mightbe desirable to use an entire tool of solid boron doped diamond ratherthan a film or multilayer structure.

4. Boron doped diamond is highly resistant to corrosion in acidic orbasic aqueous solutions. Boron doped polycrystalline diamond has beenused as electrodes for electrochemical synthesis of materials such asoxygen and chlorine. Polycrystalline diamond electrodes have a lifetimethat is many times that of conventional electrode materials such asgraphite or stainless steel. However, polycrystalline diamond undergoescatastrophic failure at many hours of operation. Polycrystalline diamondis composed of millions of tiny crystallites which connect to each otherat grain boundaries. These grain boundaries tend to accumulateimpurities which are slowly attacked leading to the failure. Applicanthas produced electrodes made of single crystal boron doped diamond.These electrodes have no grain boundaries and have life times which aresignificantly longer than polycrystalline diamond and show uniform wear,but no catastrophic failure. Moreover, single crystal diamond electrodescan withstand several orders of magnitude higher current thanpolycrystalline diamond without catastrophic failure or measurableerosion.

Finally, a composition of this invention can provide unique and specificsemiconducting properties useful, for example, in fabricating suchthings as tools, microtomes, cutting tools for detectors, and the like.

The doped layer(s) of the present invention can also include situationswhere the spacing between carbon atoms is decreased rather thanincreased. Carbon is found in several isotopes. ¹²C is the most commonisotope while ¹³C is about 1% abundance. Diamond that consists of all¹³C atoms has a smaller spacing between the carbon atoms than normaldiamond (which contains 99% ¹²C and 1% ¹³C). the dependence of thelattice constant on the isotope content of the diamond is given by theequation:

a=a _(o)−5.4×10−9×[¹³C]

where a=the lattice constant of the isotopically enriched diamond,ao=the lattice constant for undoped, natural isotope diamond, and[¹³C]=the atom fraction of ¹³C (see, H. Holloway, et. al., “Erratum:Isotope dependence of the lattice constant of diamond”, Physical ReviewB45, p. 6353 (1992).). Therefore, it is possible to deposit a layer of¹³C diamond on a ¹²C substrate and place the surface of the ¹²C diamondunder tension and the ¹³C surface layer under compression. This, inturn, leads to the following:

1. Strengthen diamond plates or crystals with the application of asingle layer, and without boron or nitrogen doping.

2. Create a heterostructure to diminish dislocations without using boronor nitrogen doped layers. This heterostructure can include alternatinglayers of undoped ¹²C and ¹³C diamond. Such a structure can end ineither a ¹²C or a ¹³C layer and then be used to grow single crystalplates of either ¹²C or ¹³C diamond.

3. Generate a layer of continuously varying ¹²C/¹³C to change from onelattice spacing to the other, thereby providing substrates for large ¹³Cdiamond crystals.

4. Since the atoms in ¹³C are closer together than conventional diamond,the ¹³C diamond is expected to be harder than conventional diamond, tothe extent that one can use ¹³C bulk crystals or layers in situationswhere it is necessary to abrade, scratch, indent or wear normal diamond.

5. It has been shown that ¹³C diamond which has less than 0.1% of ¹³Cimpurities (referred to as isotopically enriched) has an exceptionallyhigh thermal conductivity. By growing a layer of boron dopedisotopically enriched diamond on ordinary diamond, it is possible tobuild a semiconductor device in which heat was spread laterally at ahigh rate and then axially down into a heat spreader. The same could beapplied to undoped isotopically enriched diamond on ordinary diamond forthe purpose of rapid lateral removal of heat and then removing itaxially to a heat spreader. Such a structure can lead to bettertemperature control in communications lasers and other high powerdevices. In addition, alternating layers of ordinary diamond andisotopically enriched diamond can lead to a structure which has anextremely high lateral thermal conductivity compared to the verticalconductivity.

6. Since ¹²C and ¹³C have different mass, changes in isotope contentchange the bandgap of the diamond with a corresponding change inelectrical properties. (see A. T. Collins, et. al, “Indirect Energy Gapof ¹³C Diamond”, Physical Review Letters, 65, p. 891 (1990)). The bandoffset and resultant change in electrical properties can be used to makeelectrical and optical devices which are not possible without theseoffsets.

7. Since ¹³C shrinks the diamond lattice and boron or nitrogen dilatesthe lattice, it is possible to create a composition consisting of ¹²C,¹³C and heavy concentrations of boron or nitrogen (boron doping resultsin p-type semiconductor which is required for many devices). Thiscomposition can be engineered to exactly match the lattice spacing ofordinary diamond and provide structures which have the heavy boronconcentration required for device performance but having no strain. Thisapproach will provide an unstrained heterostructure such as is used inIII-V semiconductor structures.

8. Alternately, a pseudomorphic structure can be built in which layersare alternately in compression and tension and which any layer can bedoped with boron or nitrogen (or some other element). In this case, theelectrical and device properties arise from the strain inducedelectrical discontinuity.

9. Phosphorous has recently been shown to be a n-type dopant in CVDdiamond (see Koizumi, Diam Films 1997 (see S. Koizumi, et. al., “Growthand characterization of phosphorus doped n-type diamond thin films”,Diamond and Related Materials 7, p. 540-544 (1998)). However phosphorousis a significantly larger atom than carbon, nitrogen or boron (covalentradius of P is 1.57 times larger than N and 1.25 times larger than B)(see K. W. Boer, Survey of Semiconductor Physics, p. 25, van Nostrand(1990).) and this places limitations on the amount of phosphorous whichcan be incorporated into the diamond and limits its potential electricalperformance in a device. Since ¹³C shrinks the diamond lattice andphosphorous expands the lattice, it is possible to create an alloycomposition consisting of ¹²C, ¹³C and heavy concentrations ofphosphorous. This, in turn, can lead to higher phosphorousconcentrations which are more suitable for device performance.

10. By the combination of the items 8 and 9 and growing a layer of borondoped diamond and subsequently a layer of phosphorous doped diamond onecan create a p-n junction which is necessary for many semiconductordevices. The advantage of using the alloy compositions is to obtain veryhigh levels of electrically active carriers which will enable theoperation of traditional semiconductor devices in diamond. Diamondsemiconductor devices are expected to operate at higher power levels,higher temperatures and higher speeds than any other semiconductordevice material.

11. The method of this invention can be used to grow a monocrystallinediamond from normal isotope carbon and intersperse layers of ¹³C diamondfor the purpose of providing a marker for identifying the origin of thediamond as being CVD moncrystalline diamond for use in specific articlessuch as gemstones, e.g., where it is desirable to prevent confusionbetween natural and CVD grown monocrystalline diamond. Alternately, theentire monocrystal can be grown with a small amount of ¹³C carbon andalso provide a method of detection. Such a method of detection would behigh resolution x-ray diffraction, Raman spectroscopy, and massspectroscopy, each of which can be used to measure isotope content. TheRaman method, for instance, will show small changes in the crystalstructure caused by enlarging or decreasing the lattice spacing.

CVD diamond is substantially the same as natural or high pressurediamond. The method and composition of the present invention permitsingle crystal diamond to be provided in the form of plates or othersubstrates that can be used as the beginning step for producing a largenumber of diamond manufactured articles. The method can also be used toeliminate a substantial number of fabrication steps such as sawing andlapping and increased yield of useful product. Furthermore, since thequality of CVD single crystal diamond is equal to or higher than naturalor high pressure synthetic diamond, the resulting article will be ofhigh quality, have less breakage, higher optical transmission and soforth. The present invention therefore includes the use of CVD singlecrystal diamond plates, as described herein, for gemstones, scalpels,wire dies, microtomes, heat spreaders, optical windows, knives, cuttingtools, and substrates for monocrystalline diamond active devices. In aparticularly preferred embodiment, the method can be used to providediamond layers with a boron concentration ranging from about 0.005 partsper million (ppma) to about 10,000 ppma, and preferably between about0.05 parts ppma to about 3000 ppma. Such layers can be grown using theCVD technique by incorporating boron in the precursor gas atconcentrations ranging from about 100 ppma to about 300,000 ppma, andfrom about 1000 ppma to about 100,000 ppma, respectively (with respectto the carbon in the gas phase).

Diamond layers with one dopant (such as boron) can be latticed matchedto layers containing other dopants (such as nitrogen) to yieldunstrained doped layers. This can be accomplished by incorporating theappropriate relative impurity concentrations, as given by the previouslydescribed equations which relate the impurity concentrations with theresultant lattice constant change. In addition, diamond layers withtailored strain can be created by growing layers with selected impuritylevels which create the desired lattice mismatch. Such a structure canconsist of undoped layers and or layers containing boron, nitrogen, orisotopic enhancement.

Whole diamonds or individual layers can be made to have a bluecoloration which ranges from sky blue to very dark blue by adding boronto the precursor gas to yield boron concentrations ranging from about0.05 ppma to about 3000 ppma in the diamond, respectively. In suchfilms, the optical absorption coefficient for wavelengths from 450 nm to7 μm will increase as the doping level is increased and as the thicknessis increased.

Single diamonds or individual layers can be made with room temperatureelectrical resistivity ranging from about 100,000Ω-cm to about 0.01Ω-cm,and preferably from about 5000Ω-cm to about 0.02Ω-cm, by adding boron tothe precursor gas to yield boron concentrations ranging from about 0.005ppma to about 10,000 ppma (and preferably from about 0.01 ppma to about3000 ppma) in the diamond. Such boron doped layers can also be grown inconjunction with isotopically enriched layers in order to create layerjunctions which have band gap discontinuities. For example, aboron-doped ¹³C enriched layer on a natural isotope undoped layercreates a doped layer with a wider band gap than the undoped layer. Sucha layer can be expected to yield enhanced electrical properties relativeto a structure with no band gap discontinuity.

In another embodiment of the current invention the inventors havediscovered that the normal isotope single crystal diamonds which aregrown by the CVD process described herein, have a thermal conductivitysubstantially in excess of 2200 W/mK at room temperature. Measurementsof thermal conductivity were made by the application of a heat source toone side of the diamond sample and measuring the temperature on theopposite side of the sample. The equipment was calibrated by measuringaluminum, copper, and nitrogen doped diamond and found to give a thermalconductivity of 3200 W/mK at room temperature.

This is the highest thermal conductivity for a natural isotope abundancediamond (single crystal or polycrystal) ever produced by any technique.This high thermal conductivity is entirely unexpected from the prior artsince all previous natural and synthetic diamonds having the naturalisotope distribution have a thermal conductivity no higher than 2500W/mK.

The single crystal diamond produced herein has been tested as wire diesand has resulted in a larger yield of high quality wire than dies madewith natural or high pressure synthetic diamond crystals. These resultsconfirm that the articles of this invention will give increasedperformance through higher tool life.

Engineering calculations of the requirements for a heat spreader for ahigh power laser or microwave device show that the cooling effect isdirectly related to the thermal conductivity of the diamond, thethickness of the diamond and the diameter. This indicates that it ispossible to increase the performance of a heat spreader by increasingthe thermal conductivity of the diamond or to reduce the cost by usingless diamond. Furthermore, the attributes which one might expect in anexceptionally high thermal conductivity diamond are exhibited in thismaterial, including (1) high laser damage threshold, (2) enhanced wiredie life. Therefore it appears that the single crystal diamonds of thisinvention will have the performance of the isotopically enricheddiamonds but without the high cost of isotope enrichment (the cost ofthe carbon precursors in the present process is virtually negligible).

Single crystal synthetic diamond has been grown by the high pressuremethod (U.S. Pat. No. 5,127,983) and found to exhibit a maximum thermalconductivity of 2200-2500 W/mK at room temperature. High pressurediamond has been grown as free standing crystals in sizes of severalmillimeters on an edge. These large crystals are readily fabricated bypolishing into slabs by which accurate measurements of thermalconductivity can be made. Single crystal diamond is produced by the CVDmethod by growth on a single crystal seed which may originate from anatural diamond crystal, a high pressure grown diamond crystal or a CVDgrown diamond crystal. Growth of diamond on single crystal diamond seedshas been demonstrated from methane or other hydrocarbon precursors usinghot filament, microwave plasma, DC plasma and combustion flame attemperatures ranging from 800 to 1500 degrees Celsius (U.S. Pat. Nos.5,628,824, 5,387,310, 5,470,21, 5,653,952). There are no reports ofmeasurements of

thermal conductivity on these crystals in part because the above citedprocesses leave the CVD diamond crystal attached to the diamond seedcrystal and in part because the diamond crystals even if removed fromthe seed crystal would be too thin to make a meaningful measurement ofthe thermal conductivity.

A CVD crystal may be removed from its seed crystal by a number of means.The seed crystal may be removed by grinding away the seed crystal withdiamond grit in a manner which is well known in the art (Gridinsky).Alternatively the seed crystal may be removed by sawing with a diamondimpregnated diamond wheel as commonly used to cut industrial and gemdiamonds (Field). In still another method for removing the CVD diamondfrom the seed crystal a sacrificial layer is produced on the diamondseed surface, the CVD diamond is grown on top of this sacrificial layerand the sacrificial layer is subsequently removed to yield a freestanding diamond crystal plate. Methods for producing such a sacrificiallayer and removal thereof are: ion implantation to form non-diamondlayer beneath the seed surface followed by a oxidative removal processconsisting of electrolysis or heating in an oxidizing atmosphere (U.S.Pat. No. 5,587,210), building a porous structure through which diamondcan grow and which said porous structure can be removed by a combinationof acid leaching and oxidation (U.S. Pat. Nos. 5,443,032, 5,614,019); ordepositing a layer of non diamond material which can be removed byoxidation or other treatment (U.S. Pat. No. 5,290,392). In all of thesecases claims have been made and granted for growing and removing thicksingle crystal diamond from natural and high pressure diamond seedcrystals. However none of these processes have actually previously beenreduced to practice and produced thick crystals of high enough qualityfor thermal conductivity, impurity measurements or to fabricate tools,wire dies, windows or heat spreaders. In actual fact, the growth ratesdescribed in the above process patents are so slow as to economicallynot viable and would take hundreds of hours to produce a CVD diamondcrystal of any commercial utility.

In the present invention, high thermal conductivity single crystaldiamond is obtained by growing in a following manner: (1) a diamondcrystal at least about 20 micrometers, preferably 50 micrometers, andmore preferably at least about 75 or even 100 micrometers, thick isgrown on single crystal seed which can be chosen from natural diamondcrystals, synthetic high pressure diamond crystals or synthetic CVDdiamond crystals. (2) the diamond crystal is gown from hydrocarbongasses and hydrogen and may contain or not contain oxygen and is rich inatomic hydrogen (3) the CVD growth is carried out at growth rates inexcess of 10 micrometers per hour; the CVD grown crystal is removed fromthe seed crystal by grinding, sawing, use of a sacrificial layer orother removal method as might be found useful; (4) the nitrogen contentof the starting gas composition is low enough as to result in a finalCVD diamond crystal which has less than 10 to 20 ppm nitrogenincorporated into the crystal into substitutional sites and/or intointerstitial sites. When these conditions are met, then the singlecrystal diamond produced will have a thermal conductivity of greaterthan 2200 W/mK and the material will be of the size and quality requiredfor use as tools, wire dies, optical windows and heat spreaders.

Test Methods

The various parameters set forth in the present application can bedetermined in any suitable fashion. For purposes of the present claimsthese parameters are determined by the methods set forth below.

Thermal Conductivity

Methods to measure diamonds thermal conductivity have been reviewed inthe literature (see J. E. Graebner, “Thermal Measurement Techniques”, p.193-226, Handbook of Industrial Diamond and Diamond Films, M. A. Prelas,G. Popovici, and L. K. Bigelow, Editors, Marcel Dekker, Inc. (1998)).The measurement techniques include the use of steady state heatingwherein heat is applied to one part of the sample, and the temperaturedistribution on the rest of the sample is measured. If the test geometryis linear, the thermal conductivity (k) can be deduced from theequation:

k=HeatingPower/σ×ΔT/Δx

where k=thermal conductivity, HeatingPower=the power applied to heat thediamond, σ=the cross sectional area, and ΔT/Δx=the measured thermalgradient along the sample.Care must be taken to account for other heat loss mechanisms, includingradiation and alternate conduction paths. The thermal conductivity ofdiamond can also be measured using periodic heating to generate thermalwaves, and the thermal diffusivity is measured. A periodic heat sourceis applied to the sample via pulsed heating of a direct contact heateror by pulsed operation of a light source (such as a laser) which heats aregion of the sample. The thermal wave diffusion is measured usingthermocouples or infrared temperature sensors, and this allowsdetermination of the thermal diffusivity. The diffusivity (D) is relatedto the thermal conductivity (k) through the equation:

k=D×c

where k=thermal conductivity, and c=heat capacity/unit volume.

Nitrogen Content

There are a number of methods used to measure the nitrogen content indiamond, with the most appropriate technique being determined by thetype of nitrogen center found in the diamond being measured. Nitrogencan be present in a number of configurations in diamond, and the mostcommon configurations are (see C. D. Clark, A. T. Collins, and G. S.Woods, “Absorption and Luminescence Spectroscopy”, The Properties ofNatural and Synthetic Diamond, Edited by J. E. Field, Academic Press(1992).): single substitutional form (ssf); a isolated nitrogen atomreplaces one carbon atom in the lattice, the A-center; a pair ofadjacent substitutional nitrogen atoms, and the B-center; attributed tofour substitutional nitrogen atoms clustered around a lattice vacancy.The nitrogen content in diamond can be determined using massspectroscopy, optical absorption, and electron spin resonance (esr).Mass spectroscopy (such as secondary ion mass spectroscopy (SIMS)) isparticularly preferred since it can be used to detect all forms ofnitrogen in diamond, however it consumes some or all of the sample. Thespectroscopic measurement techniques are non-destructive, but they aresensitive to only certain forms of nitrogen in diamond. Infraredabsorption can be used to determine the nitrogen concentration ofvarious forms of nitrogen using the following calibration factors:

-   -   ssf: concentration=22 at. ppm/1 cm−1 absorption at 1130 cm−1    -   A center concentration=17.5 at. ppm/1 cm−1 absorption at 1130        cm−1    -   B center concentration=103.8 at. ppm/1 cm−1 absorption at 1130        cm−1

The ssf form (which is paramagnetic) can also be measured using esr bycomparing the microwave absorption to the absorption of a standard withknown spin concentration. For CVD and HPHT grown diamond, nitrogen hasbeen found to incorporate almost exclusively n the ssf and so thenitrogen concentration is determined using either the infraredabsorption (with the ssf calibration factor), esr, and/or massspectroscopy.

Boron Content

The boron content in diamond can also be determined using massspectroscopy, and using optical absorption, as well as throughelectrical measurements. The absorption at 3563 nm gives theconcentration of uncompensated boron through the equation:

[Na—Nd] (cm⁻³)=0.54×10¹⁴=abs. (1 cm⁻¹)@3563 nm

where Na=total boron concentration, and Nd=nitrogen concentration insingle substitutional form (which can be determined using one of thetechniques given above). Boron concentration can also be determined byanalyzing the electrical carrier concentration as a function oftemperature using well established equations of electrical neutrality(see J. S. Blakemore, Semiconductor Statistics, Dover Publications(1987)).

Isotope Content

The isotope content of diamond can be determined using massspectroscopy, x-ray diffraction, and Raman spectrosopy. The mostaccurate way to determine the isotopic content of a diamond is by usingmass spectrometry techniques such as SIMS or analysis of the combustionproducts made by burning the diamond. Such techniques allowdetermination of the isotope content with a demonstrated resolution onthe level of 0.01% (see T. R. Anthony, et. al., “Thermal diffusivity ofisotopically enriched ¹²C diamond” Physical Review B42, p. 1105(1990).), while SIMS measurements are known to be capable of parts perbillion resolution if appropriate measurement techniques are used andstandard samples are available (see J. M. Anthony, “Ion BeamCharacterization of Semiconductors”, Semiconductor Characterization;Present Status and Future Needs, Editors W. M. Bullis, D. G. Seiler, andA. C. Diebold, AIP Press (1996).). It must be recognized that massspectroscopy techniques require destruction

of some or all of the diamond during the measurement. Both x-raydiffraction and Raman spectroscopy (discussed below) can be used tomeasure the isotope content in diamond in a non-destructive manner, butthe accuracy of the measurement will be governed by the equipment usedand the diamond quality. High resolution x-ray diffraction can be usedto measure the lattice constant, and the measured lattice constant canbe used to determine the isotope content of the diamond using theequation given previously. Note that in order to determine the isotopecontent at atomic percent levels using x-ray analysis, the latticeconstant must be determined with a resolution of 0.00005 angstroms. Thisrequires use of high resolution x-ray diffraction equipment such as adouble crystal diffractometer with a highly perfect monochrometercrystal and including sample rotation. Such a measurement approach hasbeen described by Bartels (see W. J. Bartels, Journal of Vacuum Scienceand Technology, B1, p. 338 (1983).). To measure isotope contents with aresolution less than 1% requires further increases in measurementaccuracy. The isotope content can also be determined by measuring peakposition of the first order one-phonon Raman band, with the isotopicdependence described by K. C. Hass, et. al. (see K. C. Hass, et. al.,“Lattice dynamics and Raman spectra of isotopically mixed diamond”,Physical Review B45, pp. 7171-7182 (1992).). Note that the position ofthe Raman band shifts from 1332 cm−1 to 1281 cm−1 for a isotope changefrom 100% ¹²C to 100% ¹³C, with the position change being almost linearwith isotope content. Thus, in order to use Raman spectroscopy tomeasure 1% changes in isotope content, the Raman line position must bemeasured with a certainty which is <0.5 cm⁻¹. This requires thatmeasurements be performed using a high resolution Raman spectrometer,and requires that the diamond quality to be high enough to yield Ramanline widths which are <0.5 cm⁻¹. To measure isotope contents with aresolution less than 1% requires further increases in measurementaccuracy. Selection of the appropriate technique to use to determine theisotope content of a particular diamond will depend on the requiredaccuracy and the availability of a consumable sample, as is discussedabove.

The following non-limiting examples are provided to illustrate thepresent invention.

EXAMPLES Example 1 Growth of (100) Oriented Single Crystal Diamond onType IA Natural Diamond Using the Hot Filament Method

A natural type IA diamond single crystal is sliced on a diamondimpregnated saw to yield a substrate of (100) orientation. The substrateis polished with diamond grit suspended in olive oil and impregnatedinto a cast iron plate to achieve a surface which is free of grooves,scratches or digs. This substrate is then cleaned with hot detergent inan ultrasonic cleaner, rinsed in acetone and dried. Following cleaningthe substrate is placed in a hot filament chemical vapor depositionreactor (HFCVD) having a substrate heater consisting of a tungstenfilament held within a molybdenum holder and having a rhenium filamentapproximately 10 mm from the substrate. The reactor is evacuated to apressure of less than 10 millitorr and then backfilled to a pressure of40 torr with hydrogen having a purity of 99.999% and at a rate of 100sccm.

Power is applied to the rhenium filament to achieve a temperature of2100° C., whereupon power is applied to the substrate heater until thesubstrate reaches a temperature of 950° C. as measured by a disappearingfilament optical pyrometer. After stabilizing the temperature of thefilament and substrate for five minutes methane gas is added to the gasstream so that the final mixture is 99% hydrogen and 1% methane whilemaintaining the total gas flow at 100 sccm. Part of the hydrogen isconverted to atomic hydrogen on the surface of the filament and themethane decomposes in the presence of the atomic hydrogen on thesubstrate surface to form an epitaxial layer of diamond. Growth ismaintained for 24 hours at a rate of 1 micrometer per hour to form asingle crystal deposit of 24 micrometers thick. At the end of this timeperiod the methane flow is terminated, the filament power and substratepower are terminated and the substrate with film is cooled to roomtemperature. At this point the reactor is evacuated to remove allhydrogen and then filled with room air to atmospheric pressure.

The single crystal diamond substrate with the attached diamond film isremoved and cleaned in a mixture of chromic acid and sulfuric acid attemperature of 250° C. to remove residual non diamond carbon from thediamond surface, leaving a single crystal diamond film attached to asingle crystal seed.

An undoped single crystal diamond plate having a (100) orientation isobtained having a thickness of approximately 24 μm.

Example 2 Growth of (100) Oriented Single Crystal Diamond on Type IIANatural Diamond Using the Hot Filament Method

A natural type IIA diamond single crystal is sliced on diamondimpregnated saw to yield a substrate of (100) orientation. The substrateis polished with diamond grit suspended in olive oil and impregnatedinto a cast iron plate to achieve a surface which is flat and free ofgrooves, scratches or digs. The substrate is then cleaned with hotdetergent in an ultrasonic cleaner, rinsed in acetone and dried.Following cleaning the substrate is placed in a hot filament chemicalvapor deposition reactor (HFCVD) having a substrate heater consisting ofa tungsten filament held within a molybdenum holder and having a rheniumfilament approximately 10 mm from the substrate. The reactor isevacuated to a pressure of less than 10 millitorr and the backfilled toa pressure of 40 torr with hydrogen having a purity of 99.999% and at arate of 100 sccm.

Power is applied to the rhenium filament to achieve a temperature of2100° C. whereupon power is applied to the substrate heater until thesubstrate reaches a temperature of 950° C. as measured by a disappearingfilament optical pyrometer. After stabilizing the temperature of thefilament and substrate for five minutes methane gas which has beenenriched with respect to ¹³C is added to the gas stream so that thefinal mixture is 99% hydrogen and 1% ¹³C methane while maintaining thetotal gas flow at 100 sccm. Part of the hydrogen is converted to atomichydrogen on the surface of the filament and the methane decomposes inthe presence of the atomic hydrogen on the substrate surface to form anepitaxial layer of diamond. Growth is maintained for 24 hours at a rateof 1 micrometer per hour to form a single crystal deposit of 24micrometers thick. At the end of this time period the methane flow isterminated, the filament power and substrate power are terminated andthe substrate with film is cooled to room temperature. At this point thereactor is evacuated to remove all hydrogen and then filled with roomair to atmospheric pressure. The single crystal diamond substrate withthe attached diamond film is removed and cleaned in a mixture of chromicacid and sulfuric acid at temperature of 250° C. to remove residual nondiamond carbon from the diamond surface, leaving a single crystaldiamond film attached to a single crystal seed.

An undoped single crystal diamond plate having a (100) orientation isobtained having a thickness of approximately 24 μm.

Example 3 Growth of (100) Oriented Single Crystal Diamond on Type IBHigh Pressure Synthetic Diamond Using the Hot Filament Method

A high pressure synthetic type Ib diamond single crystal is ground andpolished to yield a substrate with a (100) orientation. The substrate isthen cleaned with hot detergent in an ultrasonic cleaner, rinsed inacetone and dried. Following cleaning the substrate is placed in a hotfilament chemical vapor deposition reactor (HFCVD) having a substrateheater consisting of a tungsten filament held within a molybdenum holderand having a rhenium filament approximately 10 mm from the substrate.The reactor is evacuated to a pressure of less than 10 millitorr andthen backfilled to a pressure of 40 torr with hydrogen having a purityof 99.999% and at a rate of 100 sccm.

Power is applied to the rhenium filament to achieve a temperature of2100° C. whereupon power is applied to the substrate heater until thesubstrate reaches a temperature of 1000° C. as measured by adisappearing filament optical pyrometer. After stabilizing thetemperature of the filament and substrate for five minutes acetone vaporis added to the gas stream so that the final mixture is 99% hydrogen and1% acetone while maintaining the total gas flow at 100 sccm. Part of thehydrogen is converted to atomic hydrogen on the surface of the filamentand the acetone decomposes in the presence of the atomic hydrogen on thesubstrate surface to form an epitaxial layer of diamond. Growth ismaintained for 48 hours at a rate of 1 micrometer per hour to form asingle crystal deposit of 48 micrometers thick. At the end of this timeperiod the acetone flow is terminated, the filament power and substratepower are terminated and the substrate with film is cooled to roomtemperature. At this point, the reactor is evacuated to remove allhydrogen and then filled with room air to atmospheric pressure.

The single crystal diamond substrate with the attached diamond film isremoved and cleaned in a mixture of chromic acid and sulfuric acid attemperature of 250° C. to remove residual non diamond carbon from thediamond surface. After cleaning the substrate and diamond are mounted ina saw having a copper blade impregnated with diamond grit, and sawingthrough the seed diamond to detach the single crystal diamond film fromthe single crystal seed.

An undoped single crystal diamond plate having a (100) orientation isobtained having a thickness of approximately 24 μm.

Example 4 Growth of (100) Oriented Boron Doped Single Crystal Diamond onType IB High Pressure Synthetic Diamond Using the Hot Filament Method

A high pressure synthetic type Ib diamond single crystal is ground andpolished to yield a substrate with a (100) orientation. The substrate isthen cleaned with hot detergent in an ultrasonic cleaner, rinsed inacetone and dried. Following cleaning the substrate is placed in a hotfilament chemical vapor deposition reactor (HFCVD) having a substrateheater consisting of a tungsten filament held within a molybdenum holderand having a rhenium filament approximately 10 mm from the substrate.The reactor is evacuated to a pressure of less than 10 millitorr andthen backfilled to a pressure of 40 torr with hydrogen having a purityof 99.999% and at a rate of 100 sccm. Power is applied to the rheniumfilament to achieve a temperature of 2100° C. whereupon power is appliedto the substrate heater until the substrate reaches a temperature of1000° C. as measured by a disappearing filament optical pyrometer. Afterstabilizing the temperature of the filament and substrate for fiveminutes acetone vapor is added to the gas stream so that the finalmixture is 99% hydrogen and 1% acetone containing 1000 parts per millionof methyl borate while maintaining the total gas flow at 100 sccm. Partof the hydrogen is converted to atomic hydrogen on the surface of thefilament and the acetone decomposes in the presence of the atomichydrogen on the substrate surface to form an epitaxial layer of diamond.Growth is maintained for 12 minutes hours at a rate of 1 micrometer perhour to form a boron doped single crystal deposit of 0.2 micrometersthick. At the end of this time period the acetone flow is terminated,the filament power and substrate power are terminated and the substratewith film is cooled to room temperature. At this point, the reactor isevacuated to remove all hydrogen and then filled with room air toatmospheric pressure. The single crystal diamond substrate with theattached diamond film is removed and cleaned in a mixture of chromicacid and sulfuric acid at temperature of 250° C. to remove residual nondiamond carbon from the diamond surface. After cleaning the substratewith the attached single crystal boron doped film diamond are mounted ina van der Pauw test system to measure the resistivity and mobility.

A boron doped single crystal film of diamond having a (100) is grownhaving a thickness of approximately 1 μm and is attached to a singlecrystal diamond substrate.

Example 5 Growth of (100) Oriented ¹³C Single Crystal Diamond on a CVDGrown Single Crystal Synthetic Diamond Using the Hot Filament Method

A polished CVD grown diamond single crystal having a (100) orientationis cleaned with hot detergent in an ultrasonic cleaner, rinsed inacetone and dried. Following cleaning the substrate is placed in a hotfilament chemical vapor deposition reactor (HCFVD) having a substrateheater consisting of a tungsten filament held within a molybdenum holderand having a rhenium filament approximately 10 mm from the substrate.The reactor is evacuated to a pressure of less than 10 millitorr andthen backfilled to a pressure of 40 torr with hydrogen having a purityof 99.999% and at a rate of 100 sccm.

Power is applied to the rhenium filament to achieve a temperature of2100° C. whereupon power is applied to the substrate heater until thesubstrate reaches a temperature of 950° C. as measured by a disappearingfilament optical pyrometer. After stabilizing the temperature of thefilament and substrate for five minutes methane gas which has beenenriched with respect to ¹³C is added to the gas stream so that thefinal mixture is 99% hydrogen and 1% ¹³C methane while maintaining thetotal gas flow at 100 sccm. Part of the hydrogen is converted to atomichydrogen on the surface of the filament and the methane decomposes inthe presence of the atomic hydrogen on the substrate surface to form anepitaxial layer of diamond. Growth is maintained for 24 hours at a rateof 1 micrometer per hour to form a single crystal deposit of 24micrometers thick. At the end of this time period the methane flow isterminated, the filament power and substrate power are terminated andthe substrate with film is cooled to room temperature. At this point thereactor is evacuated to remove all hydrogen and then filled with roomair to atmospheric pressure.

The single crystal diamond substrate with the attached diamond film isremoved and cleaned in a mixture of chromic acid and sulfturic acid attemperature of 250° C. to remove residual non diamond carbon from thediamond surface, leaving a single crystal ¹³C diamond film attached to a¹²C single crystal diamond seed.

An undoped ¹³C single crystal diamond plate having a (100) orientationis obtained having a thickness of approximately 24 μm.

Example 6 Growth of a (100) Oriented Boron and ¹³C Codoped SingleCrystal Diamond Film on a CVD Grown Single Crystal Synthetic DiamondUsing the Hot Filament Method

A polished CVD grown diamond single crystal having a (100) orientationis cleaned with hot detergent in an ultrasonic cleaner, rinsed inacetone and dried. Following cleaning the substrate is placed in a hotfilament chemical vapor deposition reactor (HCFVD) having a substrateheater consisting of a tungsten filament held within a molybdenum holderand having a rhenium filament approximately 10 mm from the substrate.The reactor is evacuated to a pressure of less than 10 millitorr andthen backfilled to a pressure of 40 torr with hydrogen having a purityof 99.999% and at a rate of 100 sccm.

Power is applied to the rhenium filament to achieve a temperature of2100° C. whereupon power is applied to the substrate heater until thesubstrate reaches a temperature of 950° C. as measured by a disappearingfilament optical pyrometer. After stabilizing the temperature of thefilament and substrate for five minutes methane gas which has beenenriched with respect to ¹³C and diborane is added to the gas stream sothat the final mixture is 99% hydrogen and 1% ¹³C methane containing 100ppm of diborane while maintaining the total gas flow at 100 sccm. Partof the hydrogen is converted to atomic hydrogen on the surface of thefilament and the methane decomposes in the presence of the atomichydrogen on the substrate surface to form an epitaxial layer of diamond.Growth is maintained for 10 minutes hours at a rate of 1 micrometer perhour to form a single crystal deposit of 0.17 micrometers thick. At theend of this time period the methane flow is terminated, the filamentpower and substrate power are terminated and the substrate with film iscooled to room temperature. At this point the reactor is evacuated toremove all hydrogen and then filled with room air to atmosphericpressure.

The single crystal diamond substrate with the attached diamond film isremoved and cleaned in a mixture of chromic acid and sulfuric acid attemperature of 250° C. to remove residual non diamond carbon from thediamond surface, leaving a boron doped single crystal ¹³C diamond filmattached to a ¹²C single crystal diamond seed.

A boron and ¹³C doped single crystal diamond film is grown attached to aCVD single crystal diamond substrate wherein the film has a (100)orientation and a thickness of approximately 0.17 μm.

Example 7 Growth of a (100) Oriented Phosphorous and ¹³C Codoped SingleCrystal Diamond Film on a CVD Grown Single Crystal Synthetic DiamondUsing the Hot Filament Method

A polished CVD grown diamond single crystal having a (100) orientationis cleaned with hot detergent in an ultrasonic cleaner, rinsed inacetone and dried. Following cleaning the substrate is placed in a hotfilament chemical vapor deposition reactor (HCFVD) having a substrateheater consisting of a tungsten filament held within a molybdenum holderand having a rhenium filament approximately 10 mm from the substrate.The reactor is evacuated to a pressure of less than 10 millitorr andthen backfilled to a pressure of 40 torr with hydrogen having a purityof 99.999% and at a rate of 100 sccm.

Power is applied to the rhenium filament to achieve a temperature of2100° C. whereupon power is applied to the substrate heater until thesubstrate reaches a temperature of 950° C. as measured by a disappearingfilament optical pyrometer. After stabilizing the temperature of thefilament and substrate for five minutes methane gas which has beenenriched with respect to ¹³C and phosphene is added to the gas stream sothat the final mixture is 99% hydrogen and 1% ¹³C methane containing 100ppm of phosphene while maintaining the total gas flow at 100 sccm. Partof the hydrogen is converted to atomic hydrogen on the surface of thefilament and the methane decomposes in the presence of the atomichydrogen on the substrate surface to form an epitaxial layer of diamond.Growth is maintained for 10 minutes hours at a rate of 1 micrometer perhour to form a single crystal deposit of 0.17 micrometers thick. At theend of this time period the methane flow is terminated, the filamentpower and substrate power are terminated and the substrate with film iscooled to room temperature. At this point the reactor is evacuated toremove all hydrogen and then filled with room air to atmosphericpressure.

The single crystal diamond substrate with the attached diamond film isremoved and cleaned in a mixture of chromic acid and sulfuric acid attemperature of 250° C. to remove residual non diamond carbon from thediamond surface, leaving a phosphorous doped single crystal ¹³C diamondfilm attached to a ¹²C single crystal diamond seed.

A phosphorous and ¹³C co doped single crystal diamond film is formed ona CVD single crystal diamond substrate having a (100) orientation,wherein the film is also (100) orientation and has a thickness ofapproximately 0.17 μm.

Example 8 Growth of a Structure Having a Boron Doped Single CrystalDiamond Layer Followed by an Undoped Single Crystal Diamond Layer on aCVD Grown Single Crystal Synthetic Diamond Using the Hot Filament Method

A polished CVD grown diamond single crystal having a (100) orientationand a thickness of 75 micrometers is cleaned with hot detergent in anultrasonic cleaner, rinsed in acetone and dried. Following cleaning thesubstrate is placed in a hot filament chemical vapor deposition reactor(HCFVD) having a substrate heater consisting of a tungsten filament heldwithin a molybdenum holder and having a rhenium filament approximately10 mm from the substrate. The reactor is evacuated to a pressure of lessthan 10 millitorr and then backfilled to a pressure of 40 torr withhydrogen having a purity of 99.999% and at a rate of 100 sccm. Power isapplied to the rhenium filament to achieve a temperature of 2100° C.whereupon power is applied to the substrate heater until the substratereaches a temperature of 950° C. as measured by a disappearing filamentoptical pyrometer. After stabilizing the temperature of the filament andsubstrate for five minutes methane gas and diborane is added to the gasstream so that the final mixture is 99% hydrogen and 1% methanecontaining 1000 ppm of diborane while maintaining the total gas flow at100 sccm. Part of the hydrogen is converted to atomic hydrogen on thesurface of the filament and the methane decomposes in the presence ofthe atomic hydrogen on the substrate surface to form an epitaxial layerof diamond. Growth is maintained for 15 minutes hours at a rate of 1micrometer per hour to form a single crystal deposit of 0.25 micrometersthick. At the end of this time, the diborane flow is terminated, and themethane flow continued for an additional 75 hours. At the end of thistime period the methane flow is terminated, the filament power andsubstrate power are terminated and the substrate with film is cooled toroom temperature. At this point the reactor is evacuated to remove allhydrogen and then filled with room air to atmospheric pressure.

The single crystal diamond substrate with the attached diamond film isremoved and cleaned in a mixture of chromic acid and sulfuric acid attemperature of 250° C. to remove residual non diamond carbon from thediamond surface, leaving a boron doped single crystal diamond layerimbedded in a 150 micrometer thick diamond crystal.

A (100) oriented single crystal diamond structure is formed having a 75μm thick undoped CVD diamond followed by a 0.25 μm thick boron dopedsingle crystal diamond layer, followed by a 75 μm thick CVD singlecrystal diamond layer.

Example 9 Growth of a Structure Having Alternating Layers of Boron DopedSingle Crystal Diamond and Undoped Layers of Undoped Single CrystalDiamond Layer on a CVD Grown Single Crystal Synthetic Diamond Using theHot Filament Method

A polished CVD grown diamond single crystal having a (100) orientationand a thickness of 75 micrometers is cleaned with hot detergent in anultrasonic cleaner, rinsed in acetone and dried. Following cleaning thesubstrate is placed in a hot filament chemical vapor deposition reactor(HCFVD) having a substrate heater consisting of a tungsten filament heldwithin a molybdenum holder and having a rhenium filament approximately10 mm from the substrate. The reactor is evacuated to a pressure of lessthan 10 millitorr and then backfilled to a pressure of 40 torr withhydrogen having a purity of 99.999% and at a rate of 100 sccm.

Power is applied to the rhenium filament to achieve a temperature of2100° C. whereupon power is applied to the substrate heater until thesubstrate reaches a temperature of 950° C. as measured by a disappearingfilament optical pyrometer. After stabilizing the temperature of thefilament and substrate for five minutes methane gas and diborane isadded to the gas stream so that the final mixture is 99% hydrogen and 1%methane containing 1000 ppm of diborane while maintaining the total gasflow at 100 sccm. Part of the hydrogen is converted to atomic hydrogenon the surface of the filament and the methane decomposes in thepresence of the atomic hydrogen on the substrate surface to form anepitaxial layer of diamond. Growth is maintained for 1.2 minutes hoursat a rate of 1 micrometer per hour to form a boron doped single crystaldeposit of 0.02 micrometers thick. At the end of this time period thediborane flow is terminated, and the methane flow continued for anadditional 1.2 minutes to produce an undoped layer of 0.02 micrometersthick. This cycle is repeated for one to ten times or more to produce asingle crystal structure of alternating boron doped and undoped layers.At the end of the growth period the methane flow is terminated, thefilament power and substrate power are terminated and the substrate withfilm is cooled to room temperature. At this point the reactor isevacuated to remove all hydrogen and then filled with room air toatmospheric pressure.

The single crystal diamond substrate with the attached diamond film isremoved and cleaned in a mixture of chromic acid and sulfuric acid attemperature of 250° C. to remove residual non diamond carbon from thediamond surface, leaving a hetero structure of alternating boron dopedand undoped single crystal diamond layers.

A single crystal diamond structure is formed consisting of tenalternating layers of boron doped and undoped diamond of which areindividually 0.02 μm thick, to total thickness being 0.2 μm thick, thestructure being the upper layer of a 75 μm thick CVD single crystaldiamond, all having a (100) orientation.

Example 10 Growth of (100) Oriented Single Crystal Diamond on a CVDGrown Single Crystal Synthetic Diamond Using the Microwave Plasma Method

A polished CVD grown diamond single crystal having a (100) orientationand a thickness of 75 micrometers is cleaned with hot detergent in anultrasonic cleaner, rinsed in acetone and dried. Following cleaning thesubstrate is placed in a microwave plasma reactor (MWCVD) having amolybdenum substrate holder. The reactor is evacuated to a pressure ofless than 10 millitorr and then backfilled to a pressure of 40 torr withhydrogen having a purity of 99.999% and at a rate of 100 sccm.

Power is applied to the microwave generator to achieve a plasma ball anda substrate temperature of 900° C. as measured by a disappearingfilament optical pyrometer. After stabilizing the plasma power andsubstrate temperature for five minutes methane gas and diborane is addedto the gas stream so that the final mixture is 99% hydrogen and 1%methane containing 1000 ppm of diborane while maintaining the total gasflow at 100 sccm. Part of the hydrogen is converted to atomic hydrogenin the plasma and the methane decomposes in the presence of the atomichydrogen on the substrate surface to form an epitaxial layer of diamond.Growth is maintained for 250 hours at a rate of 1 micrometer per hour toform a single crystal boron doped diamond of 250 micrometers thick. Atthe end of this time, the diborane flow is terminated, and the methaneflow continued for an additional 75 hours. At the end of this timeperiod the methane flow is terminated, the microwave power is terminatedand the substrate with film is cooled to room temperature. At this pointthe reactor is evacuated to remove all hydrogen and then filled withroom air to atmospheric pressure.

The single crystal diamond substrate with the attached diamond film isremoved and cleaned in a mixture of chromic acid and sulfuric acid attemperature of 250° C. to remove residual non diamond carbon from thediamond surface, leaving a boron doped single crystal diamond layer of250 micrometer thick diamond crystal attached to an undoped singlecrystal diamond seed.

An undoped single crystal diamond plate having a (100) orientation isobtained having a thickness of approximately 250 μm.

Example 11 Growth of (100) Oriented Single Crystal Diamond on a CVDGrown Single Crystal Synthetic Diamond Using the Arc Jet Method

A polished CVD grown diamond single crystal having a (100) orientationand a thickness of 75 micrometers is cleaned with hot detergent in anultrasonic cleaner, rinsed in acetone and dried. Following cleaning thesubstrate is placed in an arc jet microwave plasma reactor (MPCVD)having a molybdenum substrate holder. The reactor is evacuated to apressure of less than 10 millitorr and then backfilled to a pressure of100 torr with hydrogen having a purity of 99.999% and at a rate of 5000sccm.

Power is applied to produce an arc in the hydrogen stream and asubstrate temperature of 900° C. as measured by a disappearing filamentoptical pyrometer. After stabilizing the arc power and substratetemperature for five minutes methane gas is added to the chamber so thatthe final mixture is 99% hydrogen and 1% methane while maintaining thetotal gas flow at 5000 sccm. Part of the hydrogen is converted to atomichydrogen in the gas stream and the methane decomposes in the presence ofthe atomic hydrogen on the substrate surface to form an epitaxial layerof diamond. Growth is maintained for 25 hours at a rate of 10micrometers per hour to form a single crystal undoped diamond of 250micrometers thick. At the end of this time period the methane flow isterminated, the arc power is terminated and the substrate with film iscooled to room temperature. At this point the reactor is evacuated toremove all hydrogen and then filled with room air to atmosphericpressure.

The single crystal diamond substrate with the attached diamond film isremoved and cleaned in a mixture of chromic acid and sulfuric acid attemperature of 250° C. to remove residual non diamond carbon from thediamond surface, leaving an undoped single crystal diamond layer of 250micrometer thick diamond crystal attached to an undoped single crystaldiamond seed.

An undoped single crystal diamond plate having a (100) orientation isobtained having a thickness of approximately 250 μm.

Example 12 Growth of Single Crystal Diamond on a CVD Grown SingleCrystal Synthetic Diamond Using the Combustion Method

A polished CVD grown diamond single crystal having a (100) orientationand a thickness of 75 micrometers is cleaned with hot detergent in anultrasonic cleaner, rinsed in acetone and dried. Following cleaning thesubstrate is placed in an combustion flame reactor (CFCVD) having awater cooled molybdenum substrate holder and operating at atmosphericpressure. A gas mixture of acetylene and oxygen is utilized to heat thesubstrate to 1000° C. as measured by a disappearing filament opticalpyrometer. After stabilizing the flame and substrate temperature forfive minutes, the acetylene concentration is raised so that thecomposition is carbon rich and so that diamond growth begins. Part ofthe hydrogen is converted to atomic hydrogen in the flame and theacetylene and other hydrocarbons decomposes in the presence of theatomic hydrogen on the substrate surface to form an epitaxial layer ofdiamond. Growth is maintained for 25 hours at a rate of 20 micrometerper hour to form a single crystal undoped diamond of 500 micrometersthick. At the end of this time period the acetylene and oxygen flow areterminated and the substrate with film is cooled to room temperature.

The single crystal diamond substrate with the attached diamond film isremoved and cleaned in a mixture of chromic acid and sulfuric acid attemperature of 250° C. to remove residual non diamond carbon from thediamond surface, leaving an undoped single crystal diamond layer of 500micrometer thick diamond crystal attached to an undoped single crystaldiamond seed. An undoped single crystal diamond plate having a (100)orientation is obtained having a thickness of approximately 500 μm.

Example 13 Growth of (110) Oriented Single Crystal Diamond on a CVDGrown Single Crystal Synthetic Diamond Using the Hot Filament Method

A natural type IA diamond single crystal is sliced on a diamondimpregnated saw to yield a substrate of (110) orientation. The substrateis polished with diamond grit suspended in olive oil and impregnatedinto a cast iron plate to achieve a surface which is free of grooves,scratches or digs. The substrate is then cleaned with hot detergent inan ultrasonic cleaner, rinsed in acetone and dried. Following cleaningthe substrate is placed in a hot filament chemical vapor depositionreactor (HFCVD) having a substrate heater consisting of a tungstenfilament held within a molybdenum holder and having a rhenium filamentapproximately 10 mm from the substrate. The reactor is evacuated to apressure of less than 10 millitorr and then backfilled to a pressure of40 torr with hydrogen having a purity of 99.999% and at a rate of 100sccm.

Power is applied to the rhenium filament to achieve a temperature of2100° C. whereupon power is applied to the substrate heater until thesubstrate reaches a temperature of 950° C. as measured by a disappearingfilament optical pyrometer. After stabilizing the temperature of thefilament and substrate for five minutes methane gas is added to thetemperature of the filament and substrate for five minutes methane gasis added to the gas stream so that the final mixture is 99% hydrogen and1% methane while maintaining the total gas flow at 100 sccm. Part of thehydrogen is converted to atomic hydrogen on the surface of the filamentand the methane decomposes in the presence of the atomic hydrogen on thesubstrate surface to form an epitaxial layer of diamond. Growth ismaintained for 24 hours at a rate of 1 micrometer per hour to form asingle crystal deposit of 24 micrometers thick. At the end of this timeperiod the methane flow is terminated, the filament power and substratepower are terminated and the substrate with film is cooled to roomtemperature. At this point the reactor is evacuated to remove allhydrogen and then filled with room air to atmospheric pressure.

The single crystal diamond substrate with the attached diamond film isremoved and cleaned in a mixture of chromic acid and sulfuric acid attemperature of 250° C. to remove residual non diamond carbon from thediamond surface, leaving a single crystal diamond film attached to asingle crystal seed.

An undoped single crystal diamond plate having a (110) orientation isobtained having a thickness of approximately 24 μm.

Example 14 Growth of (111) Oriented Single Crystal Diamond on a NaturalSingle Crystal Synthetic Diamond Using the Hot Filament Method

A natural type IA diamond single crystal is cleaved along the (111)plane to yield a substrate of (100) orientation. The substrate ispolished with diamond grit suspended in olive oil and impregnated into acast iron plate to achieve a surface which is free of grooves, scratchesor digs. This substrate is then cleaned with hot detergent in anultrasonic cleaner, rinsed in acetone and dried. Following cleaning thesubstrate is placed in a hot filament chemical vapor deposition reactor(HFCVD) having a substrate heater consisting of a tungsten filament heldwithin a molybdenum holder and having a rhenium filament approximately10 mm from the substrate. The reactor is evacuated to a pressure of lessthan 10 millitorr and then backfilled to a pressure of 40 torr withhydrogen having a purity of 99.999% and at a rate of 100 sccm.

Power is applied to the rhenium filament to achieve a temperature of2100° C. whereupon power is applied to the substrate heater until thesubstrate reaches a temperature of 950° C. as measured by a disappearingfilament optical pyrometer. After stabilizing the temperature of thefilament and substrate for five minutes methane gas is added to thetemperature of the filament and substrate for five minutes methane gasis added to the gas stream so that the final mixture is 99% hydrogen and1% methane while maintaining the total gas flow at 100 sccm. Part of thehydrogen is converted to atomic hydrogen on the surface of the filamentand the methane decomposes in the presence of the atomic hydrogen on thesubstrate surface to form an epitaxial layer of diamond. Growth ismaintained for 24 hours at a rate of 1 micrometer per hour to form asingle crystal deposit of 24 micrometers thick. At the end of this timeperiod the methane flow is terminated, the filament power and substratepower are terminated and the substrate with film is cooled to roomtemperature. At this point the reactor is evacuated to remove allhydrogen and then filled with room air to atmospheric pressure.

The single crystal diamond substrate with the attached diamond film isremoved and cleaned in a mixture of chromic acid and sulfuric acid attemperature of 250° C. to remove residual non diamond carbon from thediamond surface, leaving a single crystal diamond film attached to asingle crystal seed.

An undoped single crystal diamond plate having a (111) orientation isobtained having a thickness of approximately 24 um.

1. A synthetic diamond comprising a first monocrystalline diamond layerand a second monocrystalline diamond layer, the layers formed on acompatible substrate, with the first layer in contact with the secondlayer, the layers formed by chemical vapor deposition, the first diamondlayer formed from a carbon source, the second diamond layer comprisingat least one impurity or at least one carbon isotope wherein theconcentrations of the impurity or carbon isotope in the secondmonocrystalline diamond layer are selected such that the latticeconstant of the first layer and the lattice constant of the second layerare substantially identical and the properties of the layers aresubstantially identical.
 2. A synthetic diamond comprising a firstmonocrystalline diamond layer and a second monocrystalline diamond layerformed on a compatible substrate, with the first layer in contact withthe second layer, the layers formed by chemical vapor deposition, thefirst diamond layer formed from a carbon source, the second diamondlayer comprising at least one impurity or at least one carbon isotopewherein the concentrations of the impurity or carbon isotope in thesecond monocrystalline diamond layer are selected such that the latticeconstant of the first layer and the lattice constant of the second layerare mismatched such that the lattice constant is substantially less thanor substantially greater than the lattice constant of the first layer byan amount sufficient to obtain a measurable difference in propertiesbetween the layers.
 3. A method of forming a synthetic diamondcomprising forming a first monocrystalline diamond layer and a secondmonocrystalline diamond layer formed on a compatible substrate, with thefirst layer in contact with the second layer, the layers formed bychemical vapor deposition, the first diamond layer formed from a carbonsource, the second diamond layer comprising at least one impurity or atleast one carbon isotope wherein the concentrations of the impurity orcarbon isotope in the second monocrystalline diamond layer are selectedsuch that the lattice constant of the first layer and the latticeconstant of the second layer are substantially identical and theproperties of the layers are substantially identical.
 4. A method offorming a synthetic diamond comprising forming a first monocrystallinediamond layer and a second monocrystalline diamond layer formed on acompatible substrate, with the first layer in contact with the secondlayer, the layers formed by chemical vapor deposition, the first diamondlayer formed from a carbon source, the second diamond layer comprisingat least one impurity or at least one carbon isotope wherein theconcentrations of the impurity or carbon isotope in the secondmonocrystalline diamond layer are selected such that the latticeconstant of the first layer and the lattice constant of the second layerare mismatched such that the lattice constant is substantially less thanor substantially greater than the lattice constant of the first layer byan amount sufficient to obtain a measurable difference in propertiesbetween the layers.
 5. The diamond of claim 2 wherein the concentrationsof the impurity or carbon isotope in the second monocrystalline diamondlayer are selected such that the lattice constant of the first layer andthe lattice constant of the second layer are mismatched such that thelattice constant is substantially less than or substantially greaterthan the lattice constant such that Δa/a_(o) is about 0.01 to 0.0001. 6.The method of claim 4 wherein the concentrations of the impurity orcarbon isotope in the second monocrystalline diamond layer are selectedsuch that the lattice constant of the first layer and the latticeconstant of the second layer are mismatched such that the latticeconstant is substantially less than or substantially greater than thelattice constant such that Δa/a_(o) is about 0.01 to 0.0001.
 7. Thediamond of claim 2 wherein the difference in lattice constant from thefirst layer to the second layer results in a visible difference inrefractive index.
 8. The diamond of claim 2 wherein the difference inlattice constant from the first layer to the second layer results in afracture line.
 9. The diamond of claim 2 wherein the impurity has anatomic radius greater than ¹²C and the presence of the impurityincreases lattice strain compared to a layer of ¹²C.
 10. The diamond ofclaim 2 wherein the isotope has an atomic radius less than ¹²C and thepresence of the impurity increases lattice strain compared to a layer of¹²C.
 11. The diamond of claim 2 wherein there are three or more layers,the layers have alternating lattice mismatch.
 12. The diamond of claim 2wherein the first layer is in compression with respect to the secondwhich is in tension.
 13. The diamond of claim 2 wherein the first layercomprises 99% or more ¹²C and 1% or less ¹³c.
 14. The diamond of claim 2wherein the first diamond layer is made of a carbon source with naturalconcentration of isotopes and impurities.
 15. The diamond of claim 1wherein the first diamond layer is made of a carbon source with anon-natural concentration of an isotope or impurities.
 16. The method ofclaim 4 wherein the first diamond layer is made of a carbon source withnatural concentration of isotopes and impurities.
 17. The method ofclaim 3 wherein the first diamond layer is made of a carbon source witha non-natural concentration of an isotope or impurities.
 18. The diamondof claim 2 wherein the first layer and the second layer independentlyhave a thickness of about 20 to 100 micrometers.
 19. The diamond ofclaim 2 wherein the second layer comprises a boron doped diamond layerwith a critical thickness of about 1.9×10³ to 6.46×10⁹ Angstroms. 20.The diamond of claim 2 wherein the diamond is a component of asemiconductor.
 21. The diamond of claim 20 wherein the semiconductorcomprises a P-N junction, an FET, a Schottky diode or a high voltageswitch.
 22. The diamond of claim 2 wherein the diamond comprises a tool.23. The diamond of claim 22 wherein the tool comprises a cutting tool, adie, a wear plate, a bearing, a heat spreader, a microtome or a spacer.24. The diamond of claim 2 wherein the diamond comprises a quantumcomputing device.